Box annealing of steel strip coils

ABSTRACT

A box annealing method for a steel strip coil which comprises placing a steel strip coil having a projection on its side edge portion on a base plate of a box annealing furnace, and annealing the coil.

United States Patent Iwasaki et al.

BOX ANNEALING OF STEEL STRIP COlLS Inventors: Masaru lwasaki,Kitakyushu; lsoshi Tokisada, Nakama; Shinichi Miyamoto, Kitakyushu;Toshimi Kawabata, Kitakyushu; Hiroshi Sato, Kitakyushu, all of, JapanAssignee: Nippon Steel Corporation, Tokyo,

Japan Filed: June 21, 1973 Appl. No.: 371,984

Foreign Application Priority Data June 23, I972 Japan 47-62360 US. Cl.148/112; l48/l2; l48/l3;

l48/l34; 148/155; 242/78.l; 432/5; 432/6 Int. Cl.. CZld 1/26; C2ld 9/68Primary Exuminer-C. Lovell Attorney, Agent, or FirmT0ren, McGeady andStanger [57] ABSTRACT A box annealing method for a steel strip coilwhich comprises placing a steel strip coil having a projection on itsside edge portion on a base plate of a box annealing furnace, andannealing the coil.

1 Claim, 4 Drawing Figures BOX ANNEALING OF STEEL STRIP COILS Thepresent invention relates to box annealing of steel strip coils forreducing strain caused in the side edge portions of the coil,particularly strain caused in the side edge portion which contacts theannealing furnace base plate.

Generally, cold-rolled steel sheets are coiled and annealed forreleaving strain caused by cold-rolling, and in case of electrical steelsheets, the sheets are coiled and annealed after cold-rolling to thefinal size for adjustment of the chemical composition, such as, fordecarburization and denitrization or grain adjustment.

When the annealing operation is conducted by box annealing, the steelstrip coils are piled in the furnace with their coil axis beingperpendicular to the furnace base plate and annealed.

The coils box-annealed in this way are susceptible to strain caused intheir side edge portions which contact the furnace base plate, and suchstrain in the side edge portions of the annealed coils cause significantproblems if the sheets from such coils are used in a piled state, as incase of an electrical steel sheet.

Such strains will not often cause a problem in case of ordinarycold-rolled steel sheets, since the sheets are further temper rolledafter the annealing. However, in case of cold rolled steel sheets whichare not subjected to treatments, such as, temper rolling after theannealing, and particularly in case of electrical steel sheets, the sideedge portions affected by the above strain are cut off. In case thestrain-affected portions are not cut off, it is necessary to applyshape-correction treatments.

The object of the present invention is to provide a box annealing methodwhich can minimize the strain affected zone in the side edge portions ofthe steel strip.

Another object of the present invention is to provide a box annealingmethod which reduces strain in the side edge portions caused when a coldrolled steel sheet, particularly an electrical steel strip coil isannealed.

Other objects of the present invention will be clear from the followingdescriptions and the attached drawings.

For attaining the above object, the present invention has its feature inthat the steel sheet rolled in a strip form is coiled in such a mannerthat the side edge portions form projections and recessions and then thecoil is placed on the base plate of the box annealing furnace with theprojected edge portions of the coil facing to the base plate side, andthe coil is annealed with a de sired heating cycle.

The present invention will be described in more details by referring tothe attached drawing.

FIG. 1 is a cross-sectional view showing the box annealing ofa steelstrip coil, and FIG. 2 (a) (b) and (c) are cross-sectional views ofsteel strip coils according to the present invention.

Any of ordinary steel, special steel and electrical steel can be treatedby the present invention, but the present invention is particularlysuitable for annealing electrical steel strip coil, which isbox-annealed after it has been rolled to its final size. Steel stripwhich does not need subsequent shape correction, such as, temper rollingcan be obtained. In the case when the shape correction, including thetemper rolling, is done at the separate places, for example, at user'sshops, the present invention is remarkably advantageous for preventinglowering of the commercial value of the product.

The steel strip to be treated by the present invention is rolled to thefinal size by any known means. Then the steel strip is coiled while thestrip is swung left and right so that the side edge portions of thecoiled strip form projections and recessions.

In this case, the first half of the steel strip may be coiled so as toform the projection 2 and the latter half of the strip may be coiled soas to form the recession 3 as shown in FIG.2(a).

According to another coiling method, it is also possible to coil thefirst half of the strip so as to form the simple projection 2 and coilthe latter half of the strip so as to form the recession 3 having aconcave 4 and a convex 5 alternatively by swinging the strip left andright while it is coiled. (See FIG. 2(b)) According to a still anothercoiling method, the strip is coiled in such a manner that the recession4 and the projection 5 appear alternatively with a constant cyclethrough the whole course of the ceiling, but the recession 4 and theprojection S are formed with the same number of coilings or withdifferent numbers of coilings.

When the steel strip coil coiled by swinging the strip left and right soas to have projections and recessions on its side edge portions isplaced on the base plate 7 of the annealing furnace with the said sideedge portion faced to the base plate, the projection 2 or 5 serves as asupport for the coil on the base plate 7. Then the coil is annealed witha desired heating cycle.

During the course of annealing, the material to be annealed, namely asteel strip coil and the base plate 7 of the annealing furnace expand orcontract depending on the changes in the heat treatment temperature, andgenerally their expansions or contractions do not completely coincide.Thus, the lower side of the strip coil, namely the side contacting thebase plate 7 is strained due to the perpendicular load by its own weightand the horizontal load by the abrasion, and thus is very susceptible toplastic deformation at high temperatures.

When the coil is supported on the base plate by means of the projection2 or 5 formed on the side edge portion contacting the base plateaccording to the present invention, the horizontal force imposed on theside edge portion of the coil due to the expansion or contraction causedby the change in the annealing temperature can be limited only in theprojection and prevented from expanding inside the projection or tononprojected portions.

As above mentioned, it is possible to prevent expansion of the strainaffected portion of the strip coil by forming a projection on the sideedge portions of the coil to be box-annealed according to the presentinvention.

The present invention will be more clearly understood from the followingembodiments.

EXAMPLE I A grain-oriented electrical steel strip which had been rolledto its final size was coiled in such a manner that the first half of thestrip is coiled with the normal position and the latter half was coiledby displacing the strip to one side, and the thus obtained coil wasplaced in the furnace with the inside projections contacting the baseplate 7 as shown by FIG. 2(a), and box-annealed at l C.

As seen from the results shown in Table l the strain formation wasremarkably reduced by the present invention as compared with theconventional method.

EXAMPLE 2 Low-carbon cold rolled steel strip which had been cold rolledto its final size was coiled in such a manner that the first half of thecoil was coiled by displacing the strip to one side and the latter halfof the strip was coiled at the normal position while the strip was swungleft and right each ten coilingsv The thus obtained coil was placed onthe base plate 7 with the inside projections contacting the base plateas shown by HG. 2(1)), and was box-annealed. The results are shown inTable l and the strain-affected portion was remarkably reduced.

EXAMPLE 3 Grain-oriented electrical steel strip which had been coldrolled to its final size was coiled while the strip was swung left andright each 20 coilings, and the thus obtained coil was placed on thebase plate 7 of the box an nealing furnace as shown by FIG. 2(c) andannealed at 50C. The results show the strain formation was remarkablyreduced as shown in Table 1.

Table l Strain-affected Zone (Depth in strip width direction) 4 OuterMiddle lnner Portion Portion Portion Conventional Method 35 mm 26 mm 22mm Present Example l 24 mm 22 mm l8 mm invention Example 2 5 mm l3 mm H]mm Example 3 10 mm [3 mm 7 mm It should be understood that the aboveexamples do not limit the present invention, and various modificationsand changes thereof may be made within the scope of the presentinvention. For example, the projection and the recession on the sideedge portion of the coil may be formed by coiling a steel strip havingappropriate notches on one side of the strip.

What is claimed is:

l. A method for box annealing a steel strip coil and for decreasing thestrains resulting in the sheet from non-uniform annealing whichcomprises forming a coil of a steel strip such that at least one edge ofthe coil has a projection thereon which is parallel to the winding axisof the coil and is disposed about the circumference of the coil toprovide a stable support for the coil when placed on the edge having theprojection by swinging the steel strip left and right during coiling;placing the coil on a base plate of a box annealing furnace such thateach coil rests on the projection. and annealing the

1. A METHOD FOR BOX ANNEALING A STEEL STRIP COIL AND FOR DECREASING THESTRAINS RESULTING IN THE SHEET FROM NON-UNIFORM ANNEALING WHICHCOMPRISES FORMING A COIL OF A STEEL STRIP SUCH THAT AT LEAST ONE EDGE OFTHE COIL HAS A PROJECTION THEREON WHICH IS PARALLEL TO THE WINDING AXISOF THE COIL AND IS DISPOSED ABOUT THE CIRCUMFERENCE OF THE COIL TOPROVIDE A STABLE SUPPORT FOR THE COIL WHEN PLACED ON THE EDGE HAVING THEPROJECTION BY SWINGING THE STEEL STRIP LEFT AND RING DURING COILING,PLACING